The Transgenic and Knockout Animal Core is designed to provide a centralized, service oriented facility that will insure the capacity of each participating Program Project Laboratory to produce transgenic and gene-ablated mice. The Core will provide the state-of-the-art facilities and the highly skilled technical personnel required to efficiently and economically generate and maintain animals expressing either targeted genes or specific genes which have been genetically deregulated or ablated in the germline. We have assembled an experienced team responsible for injecting targeted ES cell lines into blastocysts for the production of chimeric mice, establishing breeding programs to produce germline transmission of targeted genes, maintaining and backcrossing individual colonies and preserving established lines by embryo freezing. This technology is crucial to the Program Project's goals and continues to be a major avenue for collaborations.